There's a world of difference between a dedicated e-reader and an iPhone. A dedicated e-reader just reads books - there's not much you can offer the customer to persuade them to upgrade to the newest model, just like it's really a hard sell to get someone to upgrade to the newest model of a can opener. As long as single-function devices perform their task, people are less likely to get the new model.

A iPhone isn't really a phone at all. It's a portable computer that just happens to make phone calls. Few people upgrade to the new model of the iPhone based on the telephone functionality. With computers - whether that computer is a desktop, laptop, tablet or smartphone -, there is always a "killer app" that just won't work with the previous model.

With e-books, as long as the format is supported, the reader will never become obsolete. If I dust off a Windows 95 computer, that computer will be of very little use. I could run some very old programs, but not anything new. But a dedicated e-reader will continue to work just as well until it breaks, assuming that the format isn't abandoned. There's just far less incentive to upgrade a dedicated e-reader than there is to upgrade a general purpose device.

And a world of difference between a can opener and an ereader, don't you think? ;-)

My point is, everything depends of demand and offer, and the created necessity for a device. We have been convinced that we need a phone every 2 years but we can actually keep using the one we had 5 years ago. As a matter of fact, I own a Motorola Rzr that still works like a charm.

The thing with ereaders is that the market (and demand) for multi-purpose devices is now bigger. The fact that a device can still work without changes does not necessary means it won't be upgraded for a newest one. In my opinion, the created necessity is what dictates that.

Of course, support or lack of it, can force a replacement, but in some cases it will not, like I said, with cellphones, even cars.